Huge Black Holes May Hold Keys to Galaxy Formation

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"Something very profound is going on here, and the formation of black holes and galaxies is related in some way," said Juna Kollmeier, an astrophysicist and fellow with the Observatories of the Carnegie Institution. She focuses on the theoretical side of how the structure of the universe came to be.

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"This is an exciting new wrinkle on the old concept of black holes, and that's why so many researchers are drawn to it," she said.

And mysteries do abound. Many researchers have offered theories of how supermassive black holes might have formed, but there is no consensus. Were they created in the early universe when exploding stars were larger, or are they created by the merger of galaxies with smaller black holes at their center?

There is also the puzzling question of why some are active -- feeding regularly on stars around them -- while others are nearly dormant. Ghez added to the mystery recently by reporting that some of the stars orbiting the Milky Way's central black hole are quite young, even though the galaxy is mature and its nucleus has long been dormant.

But dormancy can be temporary, as Suvi Gezari of the California Institute of Technology documented recently. Using the telescope on NASA's orbiting Galaxy Evolution Explorer -- which measures ultraviolet light from the early universe -- her team detected a distinctive flare from a distant galaxy and watched it diminish over time. They concluded that they had seen an unfortunate star stray too close to its galaxy's central black hole, where the star was torn apart and then swallowed by the force of its gravity. The bright flare -- a rarely witnessed event -- was the result of this "feeding."

"Most of these are sleeping cosmic beasts, just sitting there," Gezari said. "So we have to scan the skies to see those very rare times that there's a burst of radiation as the black hole feeds." Like Ghez and Kollmeier, she is young and female -- still somewhat unusual in astrophysics.

Her team's goal is to measure the mass of central black holes and to correlate that with the mass of the galaxies that surround them. Might the activity or dormancy of a central black hole be tied to that surprising relationship between the mass of central black holes and their surrounding galaxies, she wonders, leading a black hole to begin "feeding" when it begins to get out of balance?

David Thompson of the NASA Goddard Space Flight Center, a key astrophysicist in the agency's Gamma Ray Large Area Space Telescope (GLAST) mission -- expected to launch next year -- is studying how that connection between a black hole and its surrounding galaxy is maintained. He believes that the high-powered jets created during feedings are probably involved.

"These black holes at the center of galaxies are relatively small but are extremely massive and have a strong influence on a huge amount of space surrounding them," he said. "It looks likely that the jets have to be playing a big part in that process."

Because the jets from supermassive black holes contain substantial amounts of gamma-ray radiation, the most highly energized form, the GLAST mission is expected to answer more questions about what's happening at the center of galaxies. Thompson will be studying "blazars" in particular -- jets aimed directly toward Earth.

The fast pace of the recent discoveries is largely the result of the newer orbiting observatories and extremely powerful ground telescopes that have begun operating in the past decade. NASA's "Beyond Einstein" initiative was approved by Congress several years ago to speed development of space-based observatories and probes designed to tell us more about the early universe and the forces that ruled it.

But tight agency budgets have slowed the initiative, and most of the Beyond Einstein probes won't be launched for years, if at all. The proposed orbiting X-ray observatory Constellation-X would be especially valuable in learning more about the structure and dynamics of supermassive black holes -- measuring, for instance, the powerful spin of the accretion disk -- but that project has been put on hold.

This has black hole researchers concerned, especially since the field has turned so productive.

"Con-X is absolutely essential, or central, to our making major advances in supermassive black hole research," said Harvey Tananbaum of the Harvard-Smithsonian Astrophysical Observatory, who chairs the science team for the Constellation project. But he said he is optimistic the project will ultimately be funded, because "the science just gets stronger and stronger."